问题
I am working on a project where I need to generate approximately 1 billion GUIDs.
I know GUIDs are not guaranteed to be unique but are unique almost all of the time.
If I generated a billion GUIDs, what is the probability that there will be a match?
回答1:
http://blogs.msdn.com/b/oldnewthing/archive/2008/06/27/8659071.aspx
The .NET GUID consists of
- 60 bits of timestamp,
- 48 bits of computer identifier,
- 14 bits of uniquifier, and
- six bits are fixed
So the UUID probability quoted by Oscar does not work here. But if you create all your 1 billion GUIDs from one computer, there is no chance to get a duplicate (except you are playing with the clock ;-)
回答2:
If you are creating the GUIds from the same machine and using the same algorithm then you will not get a collision.
回答3:
http://en.wikipedia.org/wiki/Uuid#Random_UUID_probability_of_duplicates
n probability
68,719,476,736 = 2^36 = 0.0000000000000004 = 4 × 10^−16)
2,199,023,255,552 = 2^41 = 0.0000000000004 = (4 × 10^−13)
70,368,744,177,664 = 2^46 = 0.0000000004 = (4 × 10^−10)
来源：https://stackoverflow.com/questions/3138395/what-are-the-chances-of-getting-the-same-guid-in-1-billion-iterations